NEWS

Basic Knowledge of Circular Aviation Connectors

Aviation connectors (also known as circular connectors) are electromechanical components designed for electrical circuit interconnection. Their electrical specifications are the primary factor to consider during selection. Correct selection and proper application are essential to guarantee circuit stability and reliability.

Commonly referred to as connector plugs, aviation connectors are widely used across electrical systems to make or break circuit connections. While manufacturers are primarily responsible for product reliability, the wide range of models and diverse application scenarios mean proper selection by users is equally critical. Maximum service performance can only be achieved through cooperation between manufacturers and end users.

Classification of Aviation Connectors

• By frequency: High-frequency connectors, Low-frequency connectors

• By shape: Circular connectors

• By application: Cabinet-mounted connectors, audio equipment connectors, power connectors, special-purpose customized connectors

This guide focuses on the selection rules for low-frequency aviation connectors (≤ 3MHz).

1. Safety Performance Parameters

1.1 Insulation Resistance

Insulation resistance refers to the resistance formed by leakage current on the surface and interior of insulating materials when voltage is applied. Its value is affected by insulating material grade, ambient temperature, humidity, dust and surface contamination. The rated insulation resistance stated on datasheets is tested under standard atmospheric conditions; resistance will decline under harsh environments.

Calculation Formula:

Insulation Resistance (MΩ) = Applied Voltage (V) / Leakage Current (μA)

Common test voltage grades: 10V, 100V, 500V

1.2 Withstand Voltage (Dielectric Strength)

Withstand voltage is the maximum critical voltage that insulated sections (or insulation to ground) can withstand for a specified duration without electrical breakdown. Key influencing factors include contact pin spacing, creepage distance, geometric structure, insulator material, ambient temperature, humidity and atmospheric pressure.

1.3 Flame Resistance

Carrying operating current creates fire risks for connectors. Qualified aviation connectors must resist ignition and feature self-extinguishing properties in case of fire. Always choose models made with flame-retardant, self-extinguishing insulating materials.

2. Mechanical Parameters

2.1 Contact Pressure & Unmating Force

Contact pressure directly determines contact resistance and component wear. Direct measurement is difficult, so single-pin unmating force is used as an indirect indicator. For circular pin-and-socket contacts, standard test pins are 5μm smaller than the minimum diameter of male pins to test the clamping force of female contacts.

Total unmating force is normally twice the upper limit of single-pin force. Manual plugging becomes laborious when total force exceeds 50N. For testing equipment and special scenarios, zero-insertion-force or quick-release self-disconnecting connectors are available.

2.2 Mechanical Lifespan (Mating Cycles)

Standard mechanical lifespan ranges from 500 to 1,000 mating cycles. After reaching the rated cycles, contact resistance, insulation resistance and dielectric strength must remain within specification limits.

Note: The usage frequency affects actual service life; 500 cycles used within one year impose far more wear than 500 cycles spread across 10 years. Currently, mating cycle count remains the universal evaluation standard in the industry.

2.3 Contact Pin Quantity & Gender Selection

Choose pin count according to circuit demands while taking product size and total unmating force into account. More pins mean larger overall size and higher plugging force. For high-reliability applications with available installation space, dual parallel contact pins are recommended to improve connection stability.

Male pins and female sockets are interchangeable in most assemblies. For safety, female socket inserts are recommended for permanently live socket bodies, as enclosed female contacts prevent accidental human contact with live conductive parts.

2.4 Vibration, Shock and Impact Resistance

Connectors must maintain continuous electrical contact under rated vibration frequency and acceleration. Temporary circuit interruption (micro-disconnection) may occur under dynamic stress. Industry standard transient interruption thresholds: 1μs, 10μs, 100μs, 1ms, 10ms.

Judgment standard for micro-disconnection failure: A contact point is deemed faulty if the voltage drop across closed contacts exceeds 50% of the supply voltage; both voltage drop and duration must meet the threshold.

3. Connection Locking Mechanisms (Circular Connectors)

Three mainstream locking types for circular aviation connectors:

1. Threaded Locking

Most widely used design with simple manufacturing, low cost and universal compatibility. Disadvantage: slow mating speed, not suitable for frequent plugging and quick connection scenarios.

2. Bayonet Locking

Features long guide bayonet slots for fast locking. Higher manufacturing complexity and production cost.

3. Ball Detent Push-Pull Locking

Fastest connection method; linear push/pull action completes locking and release without rotation. Only applicable to small-sized connectors with low total unmating force.

4. Installation Style & Form Factor

Installation types: Front mounting, rear mounting.

Fixing methods: Rivets, machine screws, circlips, integrated snap locks.

Dual free-end connectors are defined as inline couplers (intermediate connectors).

5. Environmental Performance Parameters

5.1 Operating Temperature Range

Metal elasticity and insulation performance determine temperature tolerance. High temperature deteriorates insulation materials, reduces insulation resistance and dielectric strength, weakens contact spring elasticity and accelerates plating oxidation.

Standard working temperature: -55℃ ~ +100℃; customized high-temperature models available for extreme conditions.

5.2 Humidity Resistance

Relative humidity above 80% greatly increases risk of electrical breakdown. Moisture absorption on insulator surfaces drastically reduces insulation resistance. Long-term high humidity causes material deformation, chemical decomposition, electrolytic corrosion and cracking.

For outdoor equipment, sealed connectors complying with GB4208 IP rating standards are required for waterproof and dustproof performance.

5.3 Rapid Temperature Cycling

Temperature shock testing simulates sudden temperature shifts (cold environment to warm environment, aerospace equipment thermal changes). Extreme temperature fluctuation may cause insulator cracking and layer separation.

5.4 Low Atmospheric Pressure (High Altitude Use)

At high altitude with thin air, plastic materials release volatile gas contaminating contact pins; corona discharge risk rises while dielectric strength drops, easily triggering short circuits. Non-sealed connectors must operate with voltage derating under low-pressure high-altitude environments.

5.5 Corrosion Resistance

Select connector housing, contact metal and surface plating based on working corrosive environment:

• Salt spray environments require heavy anti-corrosion plating;

• Silver-plated contacts are not suitable for environments with sulfur dioxide;

• Anti-mold treatment is necessary for tropical humid regions.

6. Termination Methods

6.1 Soldering

Tin soldering is the mainstream solution. Reliable soldering requires complete metallic bonding between solder and contact surface. Common plating finishes for solder terminals: tin alloy, silver, gold.

Terminal styles: tab terminals, eyelet tabs, notched tabs for spring contacts; drilled arc notched terminals for pin contacts.

6.2 Crimping

Crimping forms cold-weld metallic deformation between wire and contact barrel, delivering superior mechanical strength and electrical continuity suitable for harsh environments. Crimping outperforms soldering especially for high-current applications.

Special crimping tools or automated crimp machines are mandatory. Select contact barrels matching wire gauge. Crimp joints are permanent and non-reusable after assembly.

6.3 Wire Wrapping

Conductors are tightly wound around angular wrapping posts under controlled tension to form airtight electrical contacts.

Applicable wire diameter: 0.25mm ~ 1.0mm

Elongation requirement: ≥15% for wires ≤0.5mm; ≥20% for wires ＞0.5mm

Tools: manual wrapping guns, fixed automatic wrapping machines.

6.4 Insulation Displacement Connection (IDC)

Developed in the 1960s, IDC is widely used for ribbon cables on PCB connectors. No wire stripping required: U-shaped contact blades pierce insulation and clamp copper conductors directly for stable connection. Only compatible with specified wire gauges and requires basic assembly tools.

6.5 Screw Terminal Connection

Conductors are fixed via screw terminals. Pay attention to the allowable wire cross-section range and rated torque for different screw specifications during installation.